The long term objectives of this research are to characterize the membrane properties of Muller cells and retinal astrocytes and to relate these properties to possible glial cell functions in the retina, including the regulation of extracellular pH and [K]o, the control of retinal blood flow, and the generation of the electroretinogram. Specific aims for the project period differ from previous periods and examine, primarily, pH regulation in retinal glial cells. The aims are; (1) Characterize the acid/base transport systems of amphibian and mammalian Muller cells. Hypotheses to be tested include; (i) Muller cells possess an electrogenic Na+/HCO-3 cotransport system and a Cl-/HCO-3 exchanger which are both localized tot he cell endfoot. (ii) Muller cells possess a Na+/H+ exchanger and a H+-ATPase. (2) Test the hypothesis that muller cells modulate extracellular pH (pHo) by the action of the electrogenic Na+/HCO-3 cotransporter. The hypothesis will be tested in two preparations; (i) dissociated Muller cells (Salamander and rat) and (ii) Muller cells in situ in the isolated rat retina. (3) Test the hypothesis that Muller cells regulate pHo in the retina by functioning as CO2 buffers, transporting CO2, in the form of H- and HCO-3, to the vitreous humor. (4) Characterize the acid/base transport systems of mammalian astrocytes in situ. Specific hypotheses to be tested include: (i) the acid/base transport systems of mammalian astroytes in situ have properties similar to those found in Muller cells and cultured astrocytes. (ii) the Na+/HCO-3 cotransport system of mammalian astrocytes in situ is localized in cell endfeet. (5) Test the hypothesis that glial cells regulate blood flow in the mammalian retina. Blood vessel diameter will be monitored in the isolated rat retina as the membrane potential of glial cells is modulated by current injection. Acid/base transport systems will be characterized by monitoring intracellular and extracellular pH with ratio imaging of pH-sensitive indicator eyes. Measurements in dissociated salamander and rat muller cells will be made by imaging the dye BCECF with inverted fluorescence microscopy. In situ measurements in the isolated rat retina will be made by confocal imaging of the dye SNARF-1. Elucidating the basic membrane properties of Muller cells and retinal astrocytes is necessary for understanding the ole that these cells play in retinal function under normal and pathological condiitons, including retinitis pigmentosa and macular dystrophy.